Sheath for bunch of wires

ABSTRACT

A sheath for a bundle of wires includes a layer of cellular material and a layer of reinforcing material. The cellular material layer is a plastic foam layer containing at least 80% of closed cells, and the reinforcing material layer is a nonwoven layer. The layers are made of the same material.

The present invention relates to the sheathing of bunches or bundles,especially bundles of electrical conductors in motor vehicles.

PRIOR ART

In motor vehicles in particular, electrical conductors are beingincreasingly used because of the many new functions that are offered tousers, such as, for example, the operation of window lifters, seatadjustments and centralized locking. The numerous electricallyconducting wires are grouped together into bundles so as to limit thespace occupied in the various parts of the vehicle. However, groupingthem into bundles has also raised the problem of seeking and finding themeans of producing suitable sheaths able to receive and protect the wirebundles in an effective manner. More particularly, the sheath mustwithstand the temperatures developed, for example, in the enginecompartment, must be sealed, so as to isolate the wire bundles, mustexhibit acoustic insulation properties, so as to reduce to a minimum thenoise which could be perceived by the users, and finally must have goodmechanical strength in order to prevent premature wear due to rubbing onthe structure of the vehicle to which the sheath is fixed. Such a listis far from being exhaustive.

Various techniques are known which allow the bundled wires to be held inplace in motor vehicles:

the conventional method consists in taping the wire bundle using anadhesive or non-adhesive tape which is wound, by turning around thebundle, in order to form a winding with overlapping turns; this methodmakes it possible to obtain well-grouped bundles but requires bulkymachines and its productivity is limited;

another method consists in using longitudinally split ringed sheathsinto which the wires are introduced by forcing the slit to open, whichslit then closes up by virtue of the elasticity of the rings. This typeof sheath may be made of a polyamide, which gives it good temperatureresistance and makes it possible for it to be used in car enginecompartments. However, these sheaths have many drawbacks: theirstiffness prevents them from being bent to a small radius, the edges ofthe slit and the ends are sharp and may injure the fingers of operatorsand the insulating protection for the wires; it is practicallyimpossible to close the slit in a sealed manner and the wires maygenerate noise by impact with the wall of the sheath if the latter isnot covered on the inside with a damping material;

a third known method uses strips of flexible material which are foldedin the form of a gutter around the wires and the two edges of which thenhave to be joined together in order to provide a sheath. A tape, coatedwith adhesive on its inner face, may be used and the two edges may bejoined together by bringing the two adhesive edges face to face in orderto obtain an assembly in the form of a flag, or, according to anothermethod of assembly described in FR-2,664,850, a strip of heat-sealablematerial may be used, the two edges of which are welded in an autogenousmanner by means of a blast of hot air. At the present time, thematerials from which the strips intended for such a use are made arepolyethylene foams, because of their good flexibility and theirheat-sealability. Since the mechanical strength of this material is low,it is proposed to use a polyethylene foam reinforced for a polyamidemesh: the mesh structure for the reinforcement is necessary so that theface of each of the edges can be welded together when the two edges ofthe sheath overlap. By using closed-cell polyethylene foams, the sheathobtained is virtually sealed but, in the case of joining the two edgestogether in the form of a flag, there is a risk of the edges debondingdue to the effect of the temperature, and this joining technique resultsin bundles which are more bulky and cannot be easily passed throughperforations. Moreover, these polyethylene sheaths have a fairly lowtear resistance and do not withstand high temperatures, thereby limitingtheir field of use.

Complex laminated materials comprising a layer of foam joined to a layerof nonwoven are known and described in U.S. Pat. No. 4,851,283, GB2,112,319 and JP 05,229,045. These complex materials are used forcovering walls or for manufacturing panels for the interior lining ofvehicles, such as, for example, the headlining and/or the boots of thesaid vehicles. However, the panels are rigid and thermoformed in orderto be adapted to the shape of the support structure. In addition, thefoam layer does not necessarily comprise a percentage of closed cells asthe panels are not designed to form an impermeable barrier, the latterbeing provided by other means. The main functions of such panels are toprovide acoustic insulation and a degree of mechanical strength. This iswhy they have to be sufficiently thick, the complexes generallycomprising different materials for the foam and the nonwoven.

SUBJECT OF THE INVENTION

With the aim of obtaining sheaths for bundles in motor vehicles havingimproved performance characteristics both in terms of their use and intheir ability to provide effective protection of the electrical wires inmotor vehicles, it has been found that it could be advantageous toproduce sheaths using a laminated, flexible and conformable materialcomprising a layer of closed-cell foam intimately joined to a layer ofnonwoven, the two layers being manufactured from the same heat-sealablematerial. A strip of the composite is preferably used according to themethod in which the strip is folded into the form of a gutter and thetwo overlapping edges are welded together to form a longitudinal weldseam.

DESCRIPTION

According to one particular aspect of the present the invention, thebundles are sheathed by means of a strip of laminated complex material,the said sheathing material comprising a substantiallyliquid-impermeable first layer made of a closed-cell polyolefin foam anda nonwoven fabric second layer also made of a polyolefin.

Preferably, the layer of foam and the layer of nonwoven are bothobtained from the same type of heat-sealable material so as:

1) to allow the two layers to be joined together by a thermal means,such as a flame treatment or a hot calendering operation, without theaddition of an adhesive or of a meltable bonding material;

2) to enable the two edges of the complex to be autogenously weldedafter the sheath has been closed up around the bundle.

One of the preferred technical solutions for the technical realizationof the invention consists in using the combination of an uncrosslinkedpolypropylene foam and a nonwoven which is also made of uncrosslinkedpolypropylene. This material, which may benefit from a fireproofingtreatment so as to prevent flame spread, exhibits good heat resistanceand the sheaths obtained are satisfactory for being used in the mainparts of motor vehicles, such as, for example, the passengercompartment, the dashboard, the boot and certain areas of the enginecompartment. The fireproofing treatment may be carried out, for example:

a) by mixing flame retardants with the polypropylene during formulation;before extrusion, so as to ensure that the compounds are dispersedthroughout the mass and/or the nonwoven, or

b) by spraying the fireproofing products on the foam and/or on thenonwoven.

The layer of foam must be flexible in order to be conformed easily:polyolefin foams comprising at least 80% of closed cells, the density ofwhich is approximately 25 to 100 kg/m³ and preferably 35 to 50 kg/m³,are preferred and obtained in the form of a sheet having a thickness ofbetween 1 and 3 mm.

By way of example, the extruded uncrosslinked polypropylene foams,consisting mainly of closed cells, are very suitable for carrying outthe invention; these sheets, which have a high degree of closed cellsand a surface which forms a skin, are virtually impermeable to liquidsand make it possible to obtain a material which, at the same time, isflexible, impervious and soundproofing. As indicated above, it isadvantageous to use a polyolefin foam treated in order to be fireproofand the sheets of fireproofed polypropylene foam used for manufacturingthe material are commercially available.

The function of the layer of nonwoven material is to improve themechanical strength (tensile strength and tear strength) and the surfaceappearance of the complex. Although it is possible to use differentconstituents, it is preferred to use a polyolefin nonwoven material ofthe same type as the constituent of the foam sheet; this choice makes itpossible to obtain a homogeneous complex which can be assembled by hotcalendering without the addition of an adhesive: thus, sheathsconsisting of a single type of material, (for example polypropylene) areobtained which can thus be easily recycled. In order to obtain asatisfactory complex, a layer of nonwoven material having a thickness ofapproximately 0.3 to 0.8 mm and a mass per unit area of approximately 20to 200 g/m², and preferably 50 to 150 g/m², is used; secondarily, thelayer of nonwoven material may have received a fireproofing treatmentusing flame-spread retarders. It is also possible to use nonwoventextiles which have undergone a heat treatment (for example, at certainspots) which is intended to improve the mechanical strength. A preferredheat treatment is that which forms a check pattern on the nonwoven andwhich is designated as being a spot treatment. The check pattern may beobtained by means of a hot knurled roll which rotates against a flat(smooth) roll. Such a treatment increases the mechanical strength(tensile strength and tear strength) of the nonwoven, which is thendesignated as being heat-set.

The two layers may be joined together by any known method, such as byadhesives, heat-sealing films, flame treatment or hot calendering. It ispreferred to use complexes assembled by hot calendering, which avoid theaddition of adhesives and ensure that the assembly is temperature-stableand that the material is homogeneous.

According to the invention, the complex formed from the combination of alayer of foam and a layer of nonwoven is used to manufacture sheaths forwire bundles. The sheathing methods employed with this complex arepreferably the methods using a strip of the complex, which is foldedaround the bundle and welded in an autogenous manner by means of a blastof hot air. Such a method is described, for example, in FR 2,664,850.

According to this method, the strip is placed parallel to and under thewire bundle, the foam side being against the wires. Passing the stripthrough the shaping unit folds it around the wires until the two edgesof the strip partly overlap. A blast of hot air is then sent between thetwo edges so as to reach the softening point of the material locally,and then the two edges are brought into contact with each other so as toweld them together and to close the sheath. According to this method ofclosing the sheath, it may be seen that the external face (i.e. thenonwoven face) of the internal or covered edge (lying close to thewires) comes into contact with the internal face (i.e. the foam face) ofthe second, external or covering, edge of the strip: since the materialof the two layers is of the same type and is heat-sealable, theconditions for obtaining a solid weld of the two edges are the mostfavourable.

As a variant, when the material of the complex is thermoformable, it isalso possible to thermoform the strip in order to obtain a slit tube,then, subsequently, to introduce the wires via the slit and to weld thetwo edges of the slit, as in the previous method, in order to obtain thesheathed bundle.

According to this method of obtaining the sheath, the strip is placed sothat the layer of foam is on the inside of the sheath and the strongerlayer of nonwoven is on the outside. This arrangement has the advantageof providing a soft contact between the wires and a stronger surface onthe outside of the sheath.

According to another aspect of the invention, it may be advantageous tochoose the two layers to be of different colour, for example a whitefoam layer and the black nonwoven layer; after manufacture, the bundlewill be black in colour (the nonwoven is on the outside). The presenceof foam visible on certain parts of the bundle, which is easy toidentify because of the contrast in colour, will be able to act as atell-tale should there be a fault in the weld, or should there be weardue to extensive rubbing which would have significantly degraded thelayer of nonwoven textile.

By way of example, a sheet of complex was produced from a sheet ofuncrosslinked polypropylene foam, having a thickness of 1 mm, a densityof approximately 35 kg/m³, containing more than 80% of closed cells andbeing fireproofed, onto which was fixed, by hot calendering, a sheet ofpolypropylene nonwoven having a thickness of 0.4 mm and a mass per unitarea of 75 g/m².

The sheet of polypropylene foam is supplied by the company PSG Sentinelunder the reference Prop X® and the nonwoven is supplied by the companyDon & Low Nonwovens under the reference Daltex 1080 D3V00. The foam is atranslucent white in colour and the nonwoven, which has a chequeredappearance obtained by thermocompression, is black in colour. Accordingto the invention, this complex was cut into strips and used tomanufacture a bundle sheath by longitudinal winding and autogenouswelding of the two edges by means of hot air at 180° C. A sheathedbundle is thus obtained which is impermeable to water and to oils andsatisfies the temperature conditions corresponding to Class T2.

By way of comparison, the strength performance of a sheath obtainedaccording to the invention (thickness 1.5 mm) and the strengthperformance of a known control sheath made of polyethylene foamreinforced by a polyamide mesh (thickness 2.5 mm) were measured. Thecomparative results are given in the table below.

    ______________________________________                                                       According to the                                               Characteristics                                                                              invention   Control                                            ______________________________________                                        Thickness (mm) 1.4 to 1.6  2.4 to 2.6                                         Temperature Class                                                                            T2 (105° C.                                                                        T1 (85° C.                                                 continuous) continuous)                                        Degradation    240 h at 125° C.                                                                   240 h at 105° C.                            stability                                                                     Tensile strength                                                                             50 N/cm     13 N/cm                                            Maximum elongation                                                                           60%         30%                                                Tear strength:                                                                Longitudinal   20 N        2.5 N                                              Transverse     25 N          5 N                                              ______________________________________                                    

The results obtained show a distinct advantage of the sheath obtainedaccording to the invention, which has significantly improvedcharacteristics.

The temperature resistance of the sheath according to the inventionallows it to be assigned a "T2" classification and the significantlyimproved mechanical strength reduces the risk of tearing during themanufacture of the bundle, when fitting it into the vehicle andthroughout the lifetime of the vehicle. It should also be noted thatthese strength values are obtained with a thinner material than thecomparative product, that the processing on the sheathing machines doesnot present any more technical difficulty and that, because of thesmaller thickness, the supply of strip to the machines (and thereforethe autonomy thereof) may be considerably increased with, as directconsequence, an increase in the productivity of the wire-bundlemanufacturing workshop. Finally, since the sheath consists only ofpolypropylene, the recycling of scrap, either during manufacture or atthe end of the vehicle's life, is facilitated.

What is claimed is:
 1. Sheath for wire bundles comprising a layer ofcellular material and a layer of reinforcing material, wherein the layerof cellular material is a layer of plastic foam having at least 80% ofclosed cells, in that the layer of reinforcing material is a nonwovenand in that the layers of foam and of nonwoven are made from the samematerial.
 2. Sheath for wire bundles according to claim 1, wherein thesame material is a polyolefin.
 3. Sheath for wire bundles according toclaim 2, wherein the polyolefin is an uncrosslinked polypropylene. 4.Sheath for wire bundles according to claim 1, wherein the foam layer isfireproofed.
 5. Sheath for wire bundles according to claim 1, whereinthe layer of nonwoven is heat treated beforehand.
 6. Sheath for wirebundles according to claim 1, wherein the two layers are joined togetherusing a thermal method.
 7. Sheath for wire bundles according to one ofclaim 1, wherein the two layers are of different colour.
 8. Sheath forwire bundles according to claim 1, it is produced by folding a stripcomprising the two layers around the wire bundle and by producing alongitudinal autogenous weld along the two facing edges.
 9. Sheath forwire bundles according to claim 1, the two layers are heat-sealable.